“Without really good public transportation, it's very difficult to deal with inequality,” Kanter said. Access to just about everything associated with upward mobility and economic progress—jobs, quality food, and goods (at reasonable prices), healthcare, and schooling— relies on the ability to get around in an efficient way, and for an affordable price. A recent study from Harvard found that geographic mobility was indeed linked to economic mobility, and a 2014 study from NYU found a link between poor public-transit access and higher rates of unemployment and decreased income in New York City."

Just a US-relevant study? or global? I guess it depends on local private provision. In some Asian countries we see the cheap and cheerful tuk-tuk making transport relatively cheap, but is it still too expensive? are there any good examples of a purely private transport system offering equal transportation access to all regardless of relative income?

I heard that the Dubai transport system has a number of innovations and advantages, but it is more commercial and there is also more to work on, in terms of accessibility. I also did a little research about such system in the UK, which you can find on answershark.com/sociology.